Electric space discharge device and method of operating the same



March 23 1926. 1,577,846

A. MCL. NICOLSON ELECTRIC SPACE DISCHARGE DEVICE AND METHOD OF OPERATING THE SAME Filed Dec. 7, 1918 by A773}.

Patented Mai. 23, 1926.

UNITED STATES PATENT OFFICE.

ALEXANDER MOLEAN NICOLSON, OF NEW YORK, N. Y., ASSIGNOR T WESTERN ELEC- TRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

ELECTRIC SPACE DISCHARGE DEVICE AND METHOD OF OPERATING THE SAME.

Application filed December 27, 1918. Serial No. 268,492.

To all whom it may concern Be it known that I, ALEXANDER MoL. NICOLSON, a subject of the King of Great Britain, residing at New York, 1n the conn- 5 ty of New York and State of New York,

have invented certain new and useful Improvements in Electric Space Discharge Devices and Methods of Operating the Same, of which the following is a full, clear, concise, and exact description.

This invention relates to vacuum tubes and more particularly to the structure of the cathode of a vacuum tube and a method of and means for heating the same.

It is an object of-this invention to provide an equipotential cathode, Le, a cathode the potential of which with respect to the control electrode or the anode is substantially the same throughout its length as far as any potential drop produced by the current for energizing the cathode is concerned. This insures that all parts of the cathode will be working at an equal efficiency.

Another object of the invention is to make 26 it possible for the space current between the anode and cathode to serve to heat the latter, whereby a separate source of current for heating the cathode may be avoided.

A further object is to provide for heatso ing electrodes in an electric space discharge device by an electric space discharge from each to the other.

These objects may be accomplished by providing a connection from the output circuit back to the input circuit so as to produce high frequency oscillations in the former, and connecting the output circuit, as by a transformer, to the cathode heating circuit. A separate source of current. may be used for initially heatingthe cathode, which source may be cut out, preferably automatically, when the output current is large enough to heat the cathode. The cathode is preferably formed of two over- 46 lapping parts notelectrically connected within the tube, these parts being respectively connected to the opposite terminals of the high frequency heatlng current circuit. Since the cathode heating current is con- 59 strained to pass across the space between the cathode sections, all points in each section are at substantially the same potential, or more nearly so than would be the case if the heating current passed from one end of a filament to the other end as in the ordinary case. In the present case the cathode. heating current simultaneously leaves all points in one cathode section, passing the corresponding points in the other section rather than flowing serially along a filament and thereby producing a potential difference between the ends of a cathode section as heretofore.

These and other objects of the invention w1ll appear more fully from the following detailed description and claims, taken in connection with the accompanying drawing, which represents diagrammatically one form of the invention as applied to a smgle stage amplifier. A

Referring to the drawing, the vacuum tube 10 is shown having the usual grid 11- and plate or anode 12. A special form of cathode 13 is shown, but it is to be understood that as far as the operation of the circuit arrangement as a whole is concerned, the

cathode might/be the ordinary continuous filament. The cathode as here shown is formed inside of the tube of two electrically unconnected rods, plates or filaments of tungsten, or other suitable material closely spaced apart in substantially parallel relation. One end of each filament is free and the other ends are connected to the opposite ends of the secondary of a transformer 14, so that a high frequency alternating or pulsating current may be impressed thereon. The effect of such a current is to heat the cathode. If the tube contains a small amount of residual gas which may be ionized, a discharge may take place between the parts of the cathode, thereby heating them by bombardment. Even in a perfect vacuum, the cathode acting as a condenser will be heated by conduction of the current and the resistance of the filament. Where the frequency of the current energizing the cathode is sufficiently high, the efiect of eddy currents and under certain circumstances, of hysteresis, ma be manifest. In either case, as soon as t e filaments are sufi'iciently hot, each will be additionally heated by a thermionic discharge from the other.

A cathode made in accordance with this invention is substantially equipotential with respect to the anode and control electrode of the tube when arranged as above described. At the potentials used in the heat init. Only that element which is negative is active in emitting electrons, except at the brief instant in the high frequency cycle, of the heating current when the two elements are of the same potential. It should be further noted that in casea cathode structure is used in which there will be a substantial drop in potential between its ends, there will be no harmful effects in the operation of the tube, because of the high frequency heating current which is used.

The external portion of the space current circuit extends from the plate through the primary of the output transformer 15, the source of current 16, the coil of the relay 17 and the primary of the transformer 14: to the cathode 13. The source of current 16 is shown as a battery, but in practice it may be and usually is a direct current generator. In a shunt circuit including the primary of transformer 14 is the switch of the relay 17, and a source of high frequency current here shown schematically as an alternating current generator, but may in practice preferably be -an induction coil wh1ch may have a principal frequency of the order of 100 cycles, each cycle being composed of a train of high frequency oscillations. This current may preferably he stepped up by the transformer 11 to a voltage in the cathode heat in circuit of from 50,000 to 100,000 volts,

llihough lower potentials may be used.

The input circuit includes the grid 11, the secondary of the input transformer 19 and the cathode 13. To insure fluctuations in the space current so that they will operate the transformer 14: as described below, a feed back is provided from the output circuit to the input circuit. This feed back is shown here as being in the form of an oscillatory circuit 20 inductively related to the transformers 14 and 19, but it is to be understood that any form of oscillatory vacuum tube circuit may be used. A condenser 21 is provided having such capacity that only oscillations having a frequency above the frequency of the signals to be transmitted, may be passed. If the secondary of transformer 14 should have an appreciable resistance to the space current, it is desirable to have a choke coil 23 in shunt thereto to provide an easy path for direct current and thus preserve the equipotential character of the cathode.

potential in the cathode heating circuit. As soon as the cathode is heated to incan- 7 descence, or other temperature at which electrons are emitted from the cathode, a space current begins to flow in the tube by reason of the potential difference established by the source of current 16. The coil of the relay 17 is so adjusted that the space current passing through will open the switch against the tension of s rin 22 when the space current has attaine su cient strength to heatthe cathode through the transformer 14. Hlgh frequency oscillations are set up in the s ace current or output circuit by means 0 the feed back 20 to the input circult m a manner well understood in the art, wh1ch oscillations enable the space current to induce a high frequency high potential current in the cathode heating circuit. It will be seen therefore that the source of current 18 is used for only a very short time, and if an induction c011 be used, it can be operated by a small battery such as a single dry cell.

While a specific form of the invention has been illustrated and described, it is to be understood that the invention is not limited to th1s form, but may assume any desired form within the scope of the appended claims.

What is claimed is:

1. In a vacuum tube, an anode, a cathode, said cathode comprising two substantially parallel parts having no electrical connection with each other within the tube and a source of alternating current for heating said'cathode, said parts being connected respectively to opposite terminals of said source, each of said parts being effective to supply electrons to said anode.

2. A cathode for vacuum tubes comprising a plurality of elongated coextensive parts having no electrical connection with each other within the tube and means for supplying an alternating potential difference betwezien said parts, the average potential of sai throug out the length of said cathode.

3. In a vacuum tube, a cathode comprising two parts similar inform and havlng an equal degree of thermionic emissivity, said parts havingmo electricalconnection within the tube, an external circuit including said electrodes, and means for supplying a high frequency current to said circuit.

4. A vacuum tube eomprisin an anode a cathode and a control electro e, means for arts being substantially uniform.

its

su plyin si al waves of 'iven fre uency beiiween aid c z athode and c ntrol ele dtrode, and means for supplying higher frequency currents for heating said cathode.

5. A vacuum tube translating device having an output circuit, a cathode, said cathode being so related to said output circuit as to be heated by the output current, means for initially heating said cathode, and means operated by said output current for. rendering said. initial heating means inoperative when the output current is suflicient to heat the cathode.

6. A vacuum tube translating device having input and output circuits, means for causing said vacuum tube. to generate high fre-- quency oscillations, said means comprising means responsive to electrical var1at1ons 1n 7 said output circuit for producing electrical variations in said input circuit, and said vacuum tube having a cathode and connections whereby said generated oscillations energize said cathode to cause it to emit electrons.

7. A vacuum tube having an output circuit and a cathode, said cathode being so related to said output circuit as to be heated by the output current, a circuit coinprisin a source of current for initially heating said cathode, and a relay adapted to be energized by said output current for opening. said second circuit. v

8. A system comprising an'electron tube for transmitting electrical variatienswithin a givenfrequency range, said tube having a thermionic cathode, said system compriss ing also a circuit for supplying to saidcathode alternating heating current of frequency outside of said range, and said cir-' cuit comprising means for excluding from said cathode current of such frequency as would cause disturbance in saidtransm'ission.

9. A system comprising an electron tube for transmitting electrical signal variations of given frequency, said tube having a thermionic cathode, said system comprising also a circuit for supplying to said cathode alternating heating current of frequency higher than said signal frequency and said circuit comprising frequency selective means for excluding from said cathode heating current components of such frequency as would cause disturbance in said signal transmission.

10.-. The method of operating an electron discharge tube having therein two electrodes, which comprises passing an alternating current between said electrodes andcausing the resultant heat generated at each electrode due to said current during the half 0 cles when said electrode is serving as ano e to condition that electrode to have low negat1ve electrode impedance during the alternate half cycles. 1

11. The method of operating an electron discharge tube having therein two electrodes, whlch comprises passing such an alternating, substantially pure electron discharge.

sulting heat generated at each electrode due to said current during the half cycles when that electrode is serving as anode is sufiicient to constitute that electrode an electron emitting cathode during the alternate half cycles.

13. A vacuum tube comprising an anode, a cathode and a control electrode, means for supplying signal waves of given frequency between said cathode and control electrode, means for supplying higher frequency currents for heating said cathode, and means, external of said tube, electrically connecting one side of said cathode to one of said other electrodes.

14. The method of operating a system comprising a thermionic electron tube having an anode, a cathode and means for controlling current flow between said cathode and said anode, which comprises applying ALEXANDER MoLEAN NICOLSON. 

